GLS2 gene is composed of 18 exons, with a length of approximately 18 kbases (Pérez-Gómez et al., 2003). Position 56864728 to 56882198, minus strand (NCBI, 27165).

Transcription

Two sense GLS2 transcripts have been identified: a long canonical one containing all 18 exons (GAB, 2.4 kb)(Gómez-Fabre et al., 2000) and a short variant (LGA, 1.9 kb) lacking the first exon (Martín-Rufián et al., 2012). LGA transcript appears by alternative transcription initiation and has an alternative promoter, with its transcription start site located at 3-end of first intron of GLS2 gene. Other non-coding transcripts, containing premature stop codons, have been isolated. GLS2 transcription can be regulated by p53 and p63 tumour suppressors (Hu et al., 2010; Suzuki et al., 2010; Giacobbe et al., 2013).

Pseudogene

At least one reported pseudogene for GLS2 (GenBank: AF110329.1).

Protein

Note

To date, any GLS2 isoform has been isolated from human tissues or cells, so all information about protein structure or posttranslational modifications derive from bioinformatic analysis.

Schematic diagram of GLS2 isoforms showing the localization of predicted domains and motifs by sequence analysis.

Description

GAB transcript (1809 bps ORF) codes a 602-residues protein, with a predicted molecular mass of 66309 Da. LGA transcript (1698 bps ORF) codes a 565-residues protein, with a predicted molecular mass of 62496 Da. The precursor of LGA isoform lacks the first 61 residues at the N-terminal region of GAB precursor (coded by exon 1), but it displays an additional extension of 24 residues at the N-terminus coded by an alternative first exon. GLS2 contains a catalytic domain (glutaminase domain) of approx. 300 residues, 2 ankyrin repeats at the C-terminal region and a consensus sequence of 4 residues at the C-terminal end required for specific interaction with PDZ proteins, as alpha-syntrophin (SNT) and Glutaminase-Interacting Protein (GIP) (Olalla et al., 2001). The N-terminal end (first 14 residues) of GAB precursor contains a putative mitochondrial import presequence (Gómez-Fabre et al., 2000). It is worth mentioning the presence of a consensus LXXLL motif of interaction with nuclear receptors at N-terminal region of GLS2 (Olalla et al., 2002).

Mitochondrial. A nuclear localization has also been reported for neurons (Olalla el al., 2002).

Function

GLS2 (E.C. 3.5.1.2.) catalyzes the hydrolytic deamidation of L-glutamine to form L-glutamate and ammonium, the first step of glutaminolysis. As shown in recent works, GLS2 overexpression in glioblastoma cell lines caused a reversion of their transformed phenotype (Szeliga et al., 2009). This is in agreement with the loss of GLS2 expression in hepatocellular carcinomas (Suzuki et al., 2010) and brain tumours (Szeliga et al., 2005). So, GLS2 may play a role as tumour suppressor, in opposition to that of GLS, regulated by oncogenes and associated to tumorigenesis. However, this behavior of GLS2 is not universal, as there are some types of cancer -like cervical cancer- where upregulation of GLS2 occurs, conferring therapeutic resistance (Xiang et al., 2013).

GLS2 expression is downregulated in highly malignant glioblastoma (Szeliga et al., 2005 and 2009). One of the mechanisms involved in this gene silencing was recently demonstrated to be promoter methylation and not related to the p53 status (Szeliga et al., 2015). Human glioblastoma T98G cells stably transfected with the full GLS2 cDNA coding sequence showed a reversion of their malignant phenotype, including a marked inhibition in growth and proliferation (Szeliga et al., 2009), down-regulation of the expression of DNA-repair gene MGMT and sensitization to alkylating agents (Szeliga et al., 2012). ROS generation by treatment with oxidizing agents synergized with GLS2 overexpression in T98G glioma cells to suppress their malignant properties, including the reduction of cellular mobility (Martín-Rufián et al., 2015).

Two research groups identified GLS2 as a target for p53 tumor suppressor gene (Hu et al., 2010; Suzuki et al., 2010). GLS2 is frequently downregulated or repressed in some types of cancer, like human hepatocellular carcinoma (Yuneva et al., 2012). It is remarkable that GLS2 transcripts were almost absent or significantly decreased in hepatocellular carcinomas compared to normal liver tissue, where GLS2 is abundantly expressed (Suzuki et al. 2010). These findings support the hypothesis that repression of GLS2 is a frequent trait associated with tumorigenesis. Hence, the authors suggested a potential tumor suppressor role for GLS2 (Suzuki et al. 2010). Of interest, it has been demonstrated that GLS2 can be transcriptionally regulated by TP63, a transcription factor belonging to the p53 family (Giacobbe et al. 2013).